Uh...well, um. Actually, I'd guess it's still pretty easy to dismiss this one, given the ratio of comets to plagues. From the tenor of your contributions here, I advise you to lay in a few more kegs of critical skepticism before you set sail for Darwin's Universe.
All I'm saying is that its more intriguing now that panspermia is considered a plausible mechanism. Actually, unlike virtually everyone else on this thread, I remain agnostic. Not enough information either way but I'm open-minded enough to entertain both sides of the argument. Anyone living in the Western World in the last 100 years or so has been totally immersed in one side of the debate only. Isn't free inquiry a wonderful thing? I understand that Medieval Popes and Stalin and Mao didn't care for it.